This invention relates to improvement of a sensor node with a radio-communication function usable on a sensor net, in particular, a sensor node wearable to a human body.
Recently, a network system (hereinafter, referred to as a “sensor net”) has been studied, in which a small electronic circuit having a radio-communication function is added to a sensor to introduce various pieces of information in a real world into an information processing apparatus in real time. A wide range of applications have been considered for the sensor net. For example, there is a medical application, in which biological information such as a pulsebeat is always monitored by a small electronic circuit with a radio circuit, a processor, a sensor, and a battery integrated thereon, monitored results are sent to a diagnosis apparatus through radio-communication, and a user's health condition is determined based on the monitored results (e.g., JP 2003-102692 A, JP10-155743 A, JP 2001-070264 A, JP 2002-200051 A, JP 2003-010265 A, JP 2003-275183 A, JP 2004-139345 A, and JP 2004-312707 A).
In order to put the sensor net into practical use widely, it is important to keep an electronic circuit (hereinafter, referred to as a “sensor node”) on which a radio-communication function, a sensor, and a power supply such as a battery are mounted without maintenance for a long period of time, to allow the electronic circuit to continue to transmit sensor data, and also important to miniaturize the outer shape of the electronic circuit. Therefore, an ultra-small sensor node capable of being set anywhere is being developed. In this stage, in terms of a practical application, it is considered to be necessary that a sensor node can be used without exchanging a battery for about one year from both aspects of maintenance cost and ease of use.